Methods of assembling integrated circuit packages

ABSTRACT

Some embodiments include methods of assembling integrated circuit packages in which at least two different conductive layers are formed over a bond pad region of a semiconductor die, and in which a conductive projection associated with an interposer is bonded through a gold ball to an outermost of the at least two conductive layers. The conductive layers may comprise one or more of silver, gold, copper, chromium, nickel, palladium, platinum, tantalum, titanium, vanadium and tungsten. In some embodiments, the bond pad region may comprise aluminum, an inner of the conductive layers may comprise nickel, an outer of the conductive layers may comprise gold, the conductive projection associated with the interposer may comprise gold; and the thermosonic bonding may comprise gold-to-gold bonding of the interposer projection to a gold ball, and gold-to-gold bonding of the outer conductive layer to the gold ball. Some embodiments include integrated circuit packages.

RELATED PATENT DATA

This patent claims priority to Singapore Patent Application No.200703582-7, which was filed May 17, 2007, and which is titled“INTEGRATED CIRCUIT PACKAGES, METHODS OF FORMING INTEGRATED CIRCUITPACKAGES, AND METHODS OF ASSEMBLING INTEGRATED CIRCUIT PACKAGES”.

TECHNICAL FIELD

Integrated circuit packages, methods of forming integrated circuitpackages, and methods of assembling integrated circuit packages.

BACKGROUND

Integrated circuit packages may be formed as flip chip assemblies.Specifically, a semiconductor die may be bonded face-down (“flipped”)onto an interposer. An example prior art process for forming a flip chipassembly is described with reference to FIGS. 1 and 2.

FIG. 1 shows a semiconductor die 10 in face-down orientation, and showsan interposer 12 beneath the die.

The semiconductor die 10 comprises a base 14 supporting a plurality ofbond pad regions 16. The base 14 may comprise a semiconductor material(for instance, monocrystalline silicon) supporting any of numerousintegrated circuit components, including, for example, memorycomponents, logic components, sensor components, wiring, etc. Thevarious components are not shown in order to simplify the drawing.

Bond pad regions 16 provide electrical connection from integratedcircuit components associated with base 14 to circuitry external of thebase. The bond pad regions may comprise, consist essentially of, orconsist of aluminum or copper. The bond pad regions are shown to haveouter surfaces 17, and electrical interconnect material 18 is shownbonded to such outer surfaces. The electrical interconnect material maycomprise, consist essentially of, or consist of gold, and may be balls(as shown) bonded to the bond pad regions, or may be pieces of wirebonded to the bond pad regions.

The bond pad regions 16 may be distributed in numerous orientationsacross a surface of die 10. For example, the bond pad regions may beso-called inner bond pad regions along a central portion of the diesurface, may be so-called outer bond pad regions along non-centralportions of the die surface and connected to the inner bond pad regionsby redistribution layers, or may be a combination of inner bond padregions and outer bond pad regions.

Interposer 12 comprises a board 20 and electrical interconnects 22supported on an upper surface of the board. The interposer alsocomprises electrical interconnects 24 supported on a lower surface ofthe board. Various wiring (not shown) may extend through the board toconnect various electrical interconnects 22 with various electricalinterconnects 24. The electrical interconnects 22 are ultimately bondedto semiconductor die 10 to form an integrated circuit package comprisingthe die and interposer, and the electrical interconnects 24 areultimately utilized for electrical connection of the package to othercircuitry.

Electrical interconnects 22 may comprise, consist essentially of, orconsist of gold. Electrical interconnects 24 may comprise any suitableelectrically conductive materials or combinations of materials, and may,for example, comprise materials suitable for bonding to solder.

FIG. 2 shows the interposer 12 bonded to the semiconductor die 10. Thebonding may comprise gold-to-gold bonding between gold-containinginterconnects 22 and gold-containing interconnects 18. The gold-to-goldbonding is accomplished by pressing interconnects 18 and 22 togetherwhile subjecting the interconnects to ultrasonic energy and thermalenergy (so-called thermosonic bonding). An underfill 30 is provided in agap between die 10 and interposer 12. The underfill may comprise a filmor paste, and may, for example, comprise non-conductive paste (NCP),anisotropic conductive paste (ACP), anisotropic conductive film (ACF) ororganic solderability preservative (OSP).

A problem that can occur is that the bonding between interconnects 18and 22 may subject bond pad regions 16 to sufficient pressure to causecracking 32 (only some of which is labeled in FIG. 2) or other defectswithin the bond pad regions. Another problem that may occur is that thethermosonic energy of the thermosonic bonding may cause cratering orother defects in the bond pad regions. Yet another problem that mayoccur is that the bonding of interconnects 18 to the bond pad regions 16to form the semiconductor die construction of FIG. 1 may induce defectswithin regions 16.

It is desired to develop new methods for assembling integrated circuitpackages which avoid some or all of the above-described problems.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of a semiconductor die and interposer at a stage of aprior art process for assembling an integrated circuit package.

FIG. 2 is a view of the semiconductor die and interposer of FIG. 1 shownat a prior art processing stage subsequent to that of FIG. 1.

FIGS. 3-9 illustrates a process for preparing a semiconductor die forassembly into an integrated circuit package.

FIGS. 10 and 11 illustrate a process for assembling an integratedcircuit package comprising the semiconductor die of FIGS. 3-9 and aninterposer.

FIG. 12 shows a portion of an integrated circuit package comprising abond between a bond pad region and an interconnect of an interposer inaccordance with an embodiment.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Some embodiments include methods of providing materials across bond padsto protect the pads during subsequent thermosonic bonding. Suchmaterials may prevent, or at least substantially reduce, one or more ofthe problems discussed above in the “Background” section of thisdisclosure. An example embodiment for forming an integrated circuitpackage is described with reference to FIGS. 3-11.

Referring initially to FIG. 3, such illustrates a semiconductor die 50comprising the base 14 and bond pad regions 16 discussed above withreference to the prior art semiconductor die 10 of FIG. 1. The base may,as discussed above regarding FIG. 1, comprise integrated circuitrycontaining memory, logic, sensors, etc.

The bond pad regions 16 are shown to have outermost surfaces 17. In someembodiments, the bond pad regions may comprise, consist essentially of,or consist of aluminum or copper; and accordingly the outermost surfacesmay comprise, consist essentially of, or consist of aluminum or copper.If the bond pad regions contain aluminum, a thin oxide of aluminum (notshown) may extend across the uppermost surfaces 17 at the processingstage of FIG. 3.

Referring to FIG. 4, zinc-containing layers 52 are formed over bond padregions 16. The zinc-containing layers may be formed by first cleaningthe bond pad regions with acid (for example, one or both of sulfuricacid and hydrofluoric acid) and/or base (for example, sodium hydroxide).Such cleaning forms a fresh surface for deposition of zinc, and mayremove oxide. Subsequently, the surface may be exposed to zincate (inother words, to a zinc-containing solution, which may be, for example,cyanide-based, acid-based or alkaline-based) to deposit thin layers ofzinc (which may be monolayers) across the surfaces of the bond padregions. In some embodiments, the layers of zinc initially formed acrossthe bond pad region surfaces may have relatively large grain sizes, andmay be utilized as sacrificial layers to prepare the surfaces forsubsequent deposition of zinc-containing layers with a smaller grainsizes. Accordingly, the first zinc-containing layers may be removed withan acid (for example, nitric acid) to again expose surfaces 17 of bondpad regions 16 (FIG. 5), and then second zinc-containing layers 54 (FIG.6) may be formed by another exposure of the bond pad region surfaces tozincate.

The zinc-containing layers 54 are formed directly against the conductivematerial (for example, aluminum or copper) of the bond pad regions inthe shown embodiment of FIG. 6. Zinc-containing layers 54 may beconsidered examples of adhesion layers for adhering subsequently-formedlayers (for instance, the layers 56 discussed below with reference toFIG. 7) to the bond pad regions. The zinc-containing layers are examplesof adhesion layers, and other materials may be utilized for adhesionlayers in other embodiments. For instance, zinc-containing layers workwell for aluminum-containing surfaces, but may not work satisfactorilyfor copper-containing surfaces. Accordingly, palladium-containingadhesion layers may be utilized when the bond pad regions comprisecopper. In other embodiments, the bond pad regions may comprisematerials other than copper or aluminum, and the adhesion layers maycomprises materials other than, or in addition to, one or both of zincand palladium.

Referring next to FIG. 7, metal-containing layers 56 are formed over anddirectly against the adhesion layers 54. The metal-containing layers maycomprise one or more of Co, Cr, Ni, Pt, Ta, Ti, V and W; and may bedoped with one or both of boron and phosphorous. For instance, layers 56may comprise nickel deposited utilizing electroless depositionmethodology. In some embodiments, layers 56 may consist essentially of,or consist of such nickel; and in other embodiments layers 56 mayconsist essentially of, or consist of such nickel doped with phosphorous(the phosphorus may be present at a concentration of from about 7 atomicpercent to about 11 atomic percent).

Referring to FIG. 8, electrically conductive layers 58 are formed overand directly against electrically conductive layers 56, and balls 18 areformed directly against the conductive layers 58. The electricallyconductive layers 58 may, for example, comprise, consist essentially of,or consist of one or more of Ag, Au, Cu and Pd. Such materials may beformed by immersion methodologies, and may be doped with phosphorous orboron. For instance, the layers 58 may comprise Pd doped withphosphorous to a phosphorous concentration of from about 7 atomicpercent to about 11 atomic percent. In particular embodiments, layers 56may comprise, consist essentially of, or consist of nickel or nickeldoped with phosphorus; and layers 58 may comprise, consist essentiallyof, or consist of gold. The layers 56 and 58 may together comprise athickness of from about 0.1 micron to about 10 microns.

The balls 18 utilized in FIG. 8 may comprise any of various electricallyconductive materials, including, for example, copper or gold. The ballsmay thus comprise conventional compositions of the type described in the“Background” section of this disclosure, or may comprisenon-conventional compositions. In some embodiments, the balls will notcomprise solder, and specifically will not comprise indium or tin.

Layers 54, 56 and 58 form electrically conductive stacks over bond padregions 16. The stacks extend across the entire upper surfaces of thebond pad regions, and may be considered protective electricallyconductive caps formed across the bond pad regions. Although suchelectrically conductive caps are shown to comprise only the three layers54, 56 and 58 in the embodiment of FIGS. 3-8, in other embodiments oneor more additional layers may be inserted between adhesion layer 54 andconductive layer 56, and/or between conductive layer 56 and conductivelayer 58. For instance, the conductive stacks may comprise Ni/Pd/Au(with layers 56 and 58 being Ni and Au, respectively, and the layer ofPd being provided between them).

Since conductive layers 58 are outward of conductive layers 56 relativeto bond pad regions 16; the layers 56 may be referred to as innerconductive layers, and the layers 58 as outer conductive layers, in someembodiments.

The layers 58 are shown to comprise outermost surfaces 59. Balls 18 arebonded to the outermost surfaces 59 of layers 58. The bonding of theballs to layers 58 may be accomplished with any suitable methodology,such as, for example, thermosonic bonding. Balls 18 may comprise,consist essentially of, or consist of copper or gold; and in someembodiments the outermost surfaces 59 may comprise, consist essentiallyof, or consist of copper or gold.

Referring to FIG. 9, deformable material 60 is formed across base 14,across balls 18, and across surfaces 59 of layers 58. Deformablematerial 60 is ultimately utilized as an underfill material of a flipchip construction comprising semiconductor die 50, and may, for example,comprise one or more of a non-conductive film, non-conductive paste,anisotropically conductive film (so-called z-axis film), anisotropicallyconductive paste (so-called z-axis paste), and organic solderabilitypreservative (OSP).

Referring to FIG. 10, semiconductor die 50 is inverted and providedproximate another structure separate from the die, with such otherstructure corresponding to an interposer 12 of the type described abovewith reference to prior art FIGS. 1 and 2. The interposer comprises thebase 20 and interconnects 22 and 24 described above. The interconnects22 may comprise, consist essentially of, or consist of copper, silver,palladium or gold; and comprise outer conductive surfaces 23. Theinterconnects 22 may be considered to correspond to electricallyconductive projections or bumps in some embodiments.

Although die 50 is shown inverted in the embodiment of FIG. 10, in otherembodiments die 50 may remain in the orientation of FIG. 9 andinterposer 12 may be inverted. Also, although underfill 60 is shownformed across a surface of the die, in other embodiments some or all ofthe underfill may be formed across surfaces associated with interposer12 at the processing stage of FIG. 10. For instance, if material 60comprises OSP, such may be provided across outermost surfaces ofinterconnects 22 at the processing stage of FIG. 10. In yet otherembodiments, the underfill may be omitted, or provided at a processingstage subsequent to that of FIG. 10.

Although balls 18 are shown bonded to conductive layers 58, in otherembodiments the balls may be instead bonded to the interposer at theprocessing stage of FIG. 10.

Referring to FIG. 11, surfaces 23 of interposer 12 are pressed throughdeformable material 60 to directly contact balls 18. Once surfaces 23and balls 18 are in contact, interconnects 22 may be bonded to the ballsutilizing vibrational and/or thermal energy. The vibrational energy maybe provided to comprise a frequency of at least about one kilohertz, andthe thermal energy may correspond to a temperature of at least aboutroom temperature. In some embodiments, the bonding may comprisethermosonic bonding at a temperature of from about room temperature(about 22° C.) to about 300° C. (for example, from about roomtemperature to about 200° C.); and with a vibrational energy having afrequency of from about one kilohertz to about 240 kilohertz (forexample, a frequency of from about 40 kilohertz to about 100 kilohertz,such as a frequency of about 60 kilohertz); and for a time of less thanabout five seconds (for example, for a time of about three seconds). Inembodiments in which balls 18 initially contact surfaces 23 ofprojections 22 (in other words, contact surfaces 23 at the processingstage of FIG. 10 instead of contacting surfaces 59 of layers 58), thebonding may be accomplished with the same combination of vibrationaland/or thermal energy discussed above, but will bond the balls tosurfaces 59. In other embodiments, balls 18 may be omitted, and thevibrational and/or thermal energy may be utilized to directly bondsurfaces 23 of projections 22 to surfaces 59 of layers 58.

FIG. 11 shows surface 23 of interconnect 22 being planar, surface 59 ofouter conductive layer 58 also being planar, and balls 18 being bondedto the planar surfaces. Such leaves gaps adjacent locations where theballs contact the planar surfaces, as shown in FIG. 12. Specifically,FIG. 12 shows a portion of an integrated circuit package 100 comprisingthe various structures and layers described above with reference toFIGS. 3-11, but comprising a gap 102 identified between a surface of aball 18 and a portion of surface 59 of outer conductive layer 58. Insome embodiments, it can be advantageous to utilize z-axis conductivematerial (for example, anisotropically conductive film or paste) withinunderfill 60 so that the material 60 compressed between the surfaces ofthe ball and outer conductive layer 58 within gap 102 becomes conductivealong the axis of compression (in other words, along a shown axis 110extending within the gap between surface 59 and the ball). Theconductivity of material 60 within the gap may then provide improvedelectrical connection between conductive layer 58 and interconnect 22relative to that which would occur in the absence of conductivity ofmaterial 60. Gaps similar to gap 52 are along all locations where planarsurfaces 23 and 59 join to balls 18.

In compliance with the statute, the subject matter disclosed herein hasbeen described in language more or less specific as to structural andmethodical features. It is to be understood, however, that the claimsare not limited to the specific features shown and described, since themeans herein disclosed comprise example embodiments. The claims are thusto be afforded full scope as literally worded, and to be appropriatelyinterpreted in accordance with the doctrine of equivalents.

1. A method of assembling an integrated circuit package, comprising:providing a semiconductor die having integrated circuitry associatedtherewith, the die comprising electrically conductive bond pad regionsand electrically conductive caps over the bond pad regions, theelectrically conductive caps being along a top surface of the die andincluding at least two different conductive layers, one of the at leasttwo different conductive layers being an inner layer and the other beingan outer layer; the electrically conductive caps having first planarouter surfaces along the outer layer; providing an interposer havingelectrically conductive projections associated therewith; theprojections having second planar outer surfaces; bonding balls directlyto the first planar outer surfaces of the electrically conductive capsutilizing vibrational energy having a frequency of at least about onekilohertz; after bonding the balls to the first planar outer surfaces ofthe electrically conductive caps, providing z-axis conductive materialover the balls; the z-axis conductive material having a substantiallyplanar upper surface that extends across the balls and that extendsacross regions of the semiconductor die between the balls; the z-axisconductive material entirely surrounding exposed surfaces of the balls:the z-axis conductive material being in a non-conductive form as thez-axis conductive material is provided over and between the afterproviding the z-axis conductive material, pressing the projections ofthe interposer through the z-axis conductive material until theprojections directly contact the balls; after the projections arepressed through the z-axis conductive material, the z-axis conductivematerial filling gaps between curved regions of the balls and the firstand second planar outer surfaces, and the z-axis conductive materialbeing compressed in said gaps so that the z-axis conductive materialbecomes electrically conductive within the gaps to impose conductivityacross said gaps; and utilizing vibrational energy having a frequency ofat least about one kilohertz to bond the balls directly to the secondplanar outer surfaces of the electrically conductive projections whilecompressing the z-axis conductive material within said gaps.
 2. Themethod of claim 1 wherein the balls comprise copper.
 3. The method ofclaim 1 wherein the balls comprise gold.
 4. The method of claim 1wherein the electrically conductive bond pad regions comprise one orboth of Al and Cu; and wherein one or more of the at least two differentconductive layers of the electrically conductive caps include one ormore of Ag, Au, B, Co, Cr, Ni, P, Pd, Pt, Ta, Ti, V and W.
 5. The methodof claim 1 wherein the electrically conductive bond pad regions comprisealuminum.
 6. The method of claim 5 wherein the inner layer comprisesnickel and the outer layer comprises gold.
 7. A method of assembling anintegrated circuit package, comprising: providing a semiconductor diehaving integrated circuitry associated therewith, the die comprisingelectrically conductive bond pad regions and electrically conductivecaps over the bond pad regions; the electrically conductive caps havingfirst planar outer surfaces; providing an interposer having electricallyconductive projections associated therewith; the projections havingsecond planar outer surfaces; bonding balls directly to the first planarouter surfaces of the electrically conductive caps; after bonding theballs to the first planar outer surfaces of the electrically conductivecaps, providing underfill material over and between the balls; theunderfill material entirely surrounding exposed surfaces of the balls;the underfill material having a substantially planar upper surface thatextends across the balls and that extends across regions of thesemiconductor die between the balls; after providing the underfillmaterial, pressing the projections of the interposer through theunderfill material until the projections directly contact the balls; theunderfill being z-axis conductive material; the projections compressingthe z-axis conductive material within gaps between curved regions of theballs and the first and second planar outer surfaces to convert thez-axis conductive material within said gaps from a non-conductive formto an electrically conductive form and to thereby impose conductivityacross said gaps; and utilizing vibrational energy having a frequency ofat least about one kilohertz to bond the balls directly to the secondplanar outer surfaces of the electrically conductive projections whilecompressing the z-axis conductive material within said gaps.